GMP synthetase and gene coding for the same

ABSTRACT

A protein which has a GMP synthetase activity, a DNA which codes for the protein and a transformant which is introduced with the DNA in a form that allows expression of the protein encoded by the DNA.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel GMP synthetase and a DNA that codes for it. A microorganism that has GMP synthetase and its enzymatic activity can be used for the production of nucleic acid compounds such as guanosine 5′-monophosphate, which is useful as a raw material of seasonings and so forth.

2. Description of the Related Art

In the conventional production of nucleic acid compounds such as guanosine 51-monophosphate (also called 5′-guanylic acid, hereinafter abbreviated as “GMP”) and guanosine by fermentation, mutant strains that are imparted with adenine auxotrophy and nucleic acid analogue resistance have been utilized in a medium containing a limited amount of adenine compounds (Japanese Patent Publication (Kokoku) Nos. 55-2956/1980 and 55-45199/1980).

Usual mutagenesis treatments often introduce mutations in genes of resulting mutant strains other than a target gene. In addition, because complicated controlling mechanisms are present in the biosynthetic pathways of nucleic acid compounds, it is difficult to obtain a microorganism that produces a marked amount of a certain nucleic acid compound. Therefore, mutant strains obtained by conventional methods for breeding bacterial strains have not necessarily been satisfactory strains.

GMP is synthesized by an amination reaction catalyzed by GMP synthetase and utilizing L-glutamine as an amino group donor from 5′-inosinic acid (IMP) via xanthylic acid (XMP). Therefore, there has been proposed a method for producing GMP which utilizes Escherichia coli transformed with a GMP synthetase gene (guaA) of Escherichia coli (Japanese Patent Publication (Kokoku) No. 7-16431/1995). The guaA gene has been isolated from Bacillus subtilis (J. Bacteriol., 174, 1883-1890 (1992), EMBL/GenBank/DDBJ Accession M83691), Corynebacterium ammoniagenes (Korean Patent Publication No. 96-7743, EMBL/GenBank/DDBJ Accession Y10499), Borrelia burgdorferi (J. Bacteriol., 176, 6427-6432 (1994), EMBL/GenBank/DDBJ Accession L25883), Dictyostelium discoideum (J. Biol. Chem., 266, 16448-16452 (1991), EMBL/GenBank/DDBJ Accession M64282) and so forth.

However, no guaA gene of Brevibacterium lactofermentum (Corynebacterium glutamicum) has been known.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a guaA gene of Brevibacterium lactofermentum (Corynebacterium glutamicum) and a transformant introduced with the gene.

The inventors of the present invention actively studied in order to achieve the aforementioned object. As a result, they found a plurality of regions conserved in amino acid sequences deduced from the known guaA genes, and based on the amino acid sequences of these regions, selected a region and a sequence suitable for amplifying a guaA gene of Brevibacterium lactofermentum (Corynebacterium glutamicum) by PCR. Then, they successfully isolated a part of the guaA gene by utilizing the selected sequence, and further obtained the guaA gene in its full length. Thus, they accomplished the present invention.

That is, the present invention provides the followings.

(1) A protein defined in the following (A) or (B):

(A) a protein which has the amino acid sequence of SEQ ID NO: 2, or

(B) a protein which has the amino acid sequence of SEQ ID NO: 2 including substitution, deletion, insertion, addition or inversion of one or several amino acids, and has GMP synthetase activity.

(2) A DNA which codes for a protein defined in the following (A) or (B):

(A) a protein which has the amino acid sequence of SEQ ID NO: 2, or

(B) a protein which has the amino acid sequence of SEQ ID NO: 2 including substitution, deletion, insertion, addition or inversion of one or several amino acids, and has GMP synthetase activity.

(3) The DNA according to (2), which is a DNA defined in the following (a) or (b):

(a) a DNA which has the nucleotide sequence comprising at least the nucleotide sequence of the nucleotide numbers 887 to 2455 in SEQ ID NO: 1; or

(b) a DNA which is hybridizable with a nucleotide sequence comprising at least the nucleotide sequence of the nucleotide numbers 887 to 2455 in SEQ ID NO: 1 under a stringent condition, and codes for a protein having GMP synthetase activity.

(4) The DNA according to (3), wherein the stringent condition means a condition that washing is performed at 1×SSC, 0.1% SDS and 60° C.

(5) A transformant which is introduced with the DNA according to any one of (2) to (4) in a form that allows expression of a protein encoded by the DNA.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be explained in detail hereafter.

The DNA of the present invention is a DNA that codes for GMP synthetase derived from Brevibacterium lactofermentum (Corynebacterium glutamicum). Brevibacterium lactofermentum has now been unified into Corynebacterium glutamicum, but it may be referred to as Brevibacterium lactofermentum in the present specification for convenience.

A part of the DNA of the present invention can be obtained from chromosomal DNA of Brevibacterium lactofermentum by PCR. Primers used for the PCR can be designed as follows. That is, an amino acid sequence of a region conserved in GMP synthetases can be retrieved by alignment of amino acid sequences of the GMP synthetases deduced from nucleotide sequences of the guaA genes which have been cloned from several microorganisms, for example, Escherichia coli, Bacillus subtilis, Corynebacterium ammoniagenes, Borrelia burgdorferi, Dictyostelium discoideum and so forth. Then, the primers can be designed based on the retrieved conserved region. In this procedure, the PCR primers are designed by selecting such a region that the number of corresponding codons should become as few as possible, and referring to occurring frequency of the codons in Brevibacterium lactofermentum.

Chromosomal DNA of B. lactofermentum can be prepared by, for example, the method of Saito and Miura (Biochem. Biophys. Acta., 72, 619, (1963)), and the method of K. S. Kirby (Biochem. J., 64, 405, (1956)) or the like.

As preferred primers and PCR condition for amplification of the guaA gene, the combinations of primers and the reaction conditions used for Reactions 2, 3 and 4 shown in Table 1 can be mentioned. By using these reaction conditions, reaction products having sizes of about 0.5 kbp, about 1.2 kbp and about 0.7 kbp, respectively, can be obtained. Among these reaction products, the fragment of about 1.2 kbp overlaps the fragment of about 0.5 kbp.

Based on a partial sequence of the guaA gene obtained as described above, upstream and downstream flanking regions of the partial sequence can be obtained by the cassette-ligation mediated PCR method (Molecular and Cellular Probes, 6, 467-475) or the like, and thus a full length guaA gene can be obtained. That is, a region flanking a known region on chromosomal DNA can be obtained by ligating a cassette to a chromosomal DNA fragment digested with a suitable restriction enzyme, and amplifying it by PCR utilizing a primer corresponding to the known region and a primer corresponding to the cassette. In this procedure, by using a dephosphorylated 5′ end of-the cassette, a nick is produced at the ligation site of the chromosomal DNA fragment and the 5′ end of the cassette. Therefore, the DNA synthesis started from the cassette primer is stopped at this ligation site, and thus only DNA synthesized from the synthetic primer serves as a template for the synthesis from the cassette primer to form a complementary strand. The nucleotide sequence of the obtained amplification product is determined, then specific primers for the newly determined nucleotide sequence are synthesized, and PCR is performed by using the chromosomal DNA fragment similarly ligated to the cassette as a template. By repeating this procedure, the upstream and downstream flanking regions can be obtained. A kit utilizing this method is commercially available (TAKARA LA PCR in vitro Cloning Kit, Takara Shuzo), and it can be utilized for obtaining the DNA of the present invention.

Since the nucleotide sequences of the DNA of the present invention and the flanking regions have been revealed, the DNA of the present invention can be directly amplified by PCR utilizing oligonucleotides synthesized based on the nucleotide sequences as primers and chromosomal DNA of coryneform bacteria as a template. As such primers, oligonucleotides which have the nucleotide sequences shown in SEQ ID NO: 12 and SEQ ID NO: 13 can be mentioned. In a DNA obtained by using these primers, the SD (Shine-Dalgarno) sequence is added upstream of the region coding for GMP synthetase, and restriction enzyme recognition sites are added to the both ends. Moreover, the DNA of the present invention can also be isolated from a chromosomal DNA library by hybridization utilizing an oligonucleotide synthesized based on its nucleotide sequence as a probe.

An example of nucleotide sequence of a DNA fragment containing the DNA of the present invention, which can be obtained as described above, is shown in SEQ ID NO: 1 of Sequence Listing. In this nucleotide sequence, the region consisting of nucleotides of nucleotide numbers 887-2455 codes for GMP synthetase, which is the protein of the present invention.

The DNA of the present invention may code for GMP synthetase including substitution, deletion, insertion, addition, or inversion of one or several amino acids at one or a plurality of positions, provided that the activity of GMP synthetase encoded thereby is not deteriorated. The number of “several” amino acids differs depending on the position or the type of amino acid residues in the three-dimensional structure of the protein. This is because of the following reason. That is, some amino acids such as isoleucine and valine are amino acids having high homology to one another. The difference in such an amino acid does not greatly affect the three-dimensional structure of the protein. Therefore, the protein encoded by the DNA of the present invention may be one which has homology of not less than 80%, preferably 90% with respect to the entire amino acid residues for constituting. GMP synthetase, and which has the GMP synthetase activity. More appropriately, the number of “several” amino acids is 2 to 104, preferably 2 to 50, and more preferably 2 to 10.

Alternatively, DNA of the present invention may be DNA which has homology of not less than 60%, preferably not less than 70% and more preferably not less than 80% i z with the region consisting of nucleotides of nucleotide numbers 887-2455 in SEQ ID NO: 1 in nucleotide sequence level, provided that the protein encoded by the DNA has GMP synthetase activity.

DNA, which codes for the substantially same protein as GMP synthetase as described above, is obtained, for example, by modifying the nucleotide sequence, for example, by means of the site-directed mutagenesis method so that one or more amino acid residues at a specified site involve substitution, deletion, insertion, addition, or inversion. DNA modified as described above may be obtained by the conventionally known mutation treatment. The mutation treatment includes a method for treating DNA coding for GMP synthetase in vitro, for example, with hydroxylamine, and a method for treating a microorganism, for example, a bacterium belonging to the genus Escherichia harboring DNA coding for GMP synthetase with ultraviolet irradiation or a mutating agent such as N-methyl-N′-nitro-N-nitroguanidine (NTG) and nitrous acid usually used for the mutation treatment.

The substitution, deletion, insertion, addition, or inversion of nucleotide as described above also includes mutant or variant which naturally occurs, for example, on the basis of the individual difference or the difference in species or genus of the microorganism which harbors GMP synthetase.

The DNA, which codes for substantially the same protein as GMP synthetase, is obtained by isolating DNA which is hybridizable with DNA having, for example, a nucleotide sequence corresponding to nucleotide numbers of 887 to 2455 of the nucleotide sequence depicted in SEQ ID NO: 1 in Sequence Listing under a stringent condition, and which codes for a protein having the GMP synthetase activity, from DNA coding for GMP synthetase having mutation or from a cell harboring it. The “stringent condition” referred to herein is a condition under which so-called specific hybrid is formed, and non-specific hybrid is not formed. It is difficult to clearly express this condition by using any numerical value. However, for example, the stringent condition includes a condition under which DNA's having high homology, for example, DNA's having homology of not less than 60% are hybridized with each other, and DNA's having homology lower than the above are not hybridized with each other. Alternatively, the stringent condition is exemplified by a condition in which washing in hybridization procedure is performed at 1×SSC, 0.1% SDS, 60° C., preferably at 1×SSC, 65° C., and more preferably at 0.5×SSC, 65° C.

The gene, which is hybridizable under the condition as described above, includes those having a stop codon generated in a coding region of the gene, and those having no activity due to mutation of active center. However, such mutants can be easily removed by ligating the gene with a commercially available activity expression vector, and measuring the GMP synthetase activity in accordance with the method described above.

The protein of the present invention is a protein encoded by the aforementioned DNA of the present invention, and has the amino acid sequence shown in SEQ ID NO: 2. The protein of the present invention may have an amino acid sequence of SEQ ID NO: 2 including substitution, deletion, insertion, addition or inversion of one or several amino acids, so long as it has GMP synthetase activity.

The GMP synthetase of the present invention has an activity for catalyzing the reaction that generates GMP from XMP. In this reaction, it can utilize L-glutamine and (NH₄)₂SO₄ as an amino group donor. The measured Km values for L-glutamine and ammonia of the GMP synthetase of the present invention were about 9.6 mM and 8.2 mM, respectively.

Moreover, when L-glutamine was used as an amino group donor, the GMP synthetase of the present invention showed the maximum activity around pH 6.5. When ammonia was used as the amino group donor with a constant amount of (NH₄)₂SO₄, which was added as a source of the amino group donor, it showed the maximum activity around pH 8.0 to 9.0. The GMP synthetase of the present invention was stable for at least 15 minutes at up to about 23° C.

In a transformant which is introduced with the DNA of the present invention in a form that allows expression of the GMP synthetase encoded by the DNA, the GMP synthetase activity is enhanced compared with a cell that is not transformed with it.

The “coryneform bacteria” includes bacteria having been hitherto classified into the genus Brevibacterium but united into the genus Corynebacterium at present (Int. J. Syst. Bacteriol., 41, 255 (1981)), and include bacteria belonging to the genus Brevibacterium closely relative to the genus Corynebacterium. Examples of such coryneform bacteria include the followings.

Corynebacterium acetoacidophilum

Corynebacterium acetoglutamicum

Corynebacterium alkanolyticum

Corynebacterium callunae

Corynebacterium glutamicum

Corynebacterium lilium (Corynebacterium glutamicum)

Corynebacterium melassecola

Corynebacterium thermoaminogenes

Corynebacterium herculis

Brevibacterium divaricatum (Corynebacterium glutamicum)

Brevibacterium flavum (Corynebacterium glutamicum)

Brevibacterium immariophilum

Brevibacterium lactofermentum (Corynebacterium glutamicum)

Brevibacterium roseum

Brevibacterium saccharolyticum

Brevibacterium thiogenitalis

Brevibacterium ammoniagenes (Corynebacterium ammoniagenes)

Brevibacterium album

Brevibacterium cerinum

Microbacterium ammoniaphilum

Specifically, the following strains of these bacteria are exemplified:

Corynebacterium acetoacidophilum ATCC13870

Corynebacterium acetoglutamicum ATCC15806

Corynebacterium alkanolyticum ATCC21511

Corynebacterium callunae ATCC15991

Corynebacterium glutamicum ATCC13020, 13032, 13060

Corynebacterium lilium (Corynebacterium glutamicum) ATCC15990

Corynebacterium melassecola ATCC17965

Corynebacterium thermoaminogenes AJ12340 FERM BP-1539)

Corynebacterium herculis ATCC13868

Brevibacterium divaricatum (Corynebacterium glutamicum) ATCC14020

Brevibacterium flavum (Corynebacterium glutamicum) ATCC13826, ATCC14067

Brevibacterium immariophilum ATCC14068

Brevibacterium lactofermentum (Corynebacterium glutamicum) ATCC13665, ATCC13869

Brevibacterium roseum ATCC13825

Brevibacterium saccharolyticum ATCC14066

Brevibacterium thiogenitalis ATCC19240

Corynebacterium ammoniagenes (Brevibacterium ammoniagenes) ATCC6871

Brevibacterium album ATCC15111

Brevibacterium cerinum ATCC15112

Microbacterium ammoniaphilum ATCC15354

These strains can be provided from, for example, the American Type Culture Collection. Each strain is assigned its registration number, and one can request provision of each strain by referring to its registration number. The registration numbers corresponding to the strains are indicated on the catalog of the American Type Culture Collection (Address: 12301 Parklawn Drive, Rockville, Md. 20852, United States of America). The AJ12340 strain was deposited at the National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, Ministry of International Trade and Industry (zip code: 305-8566, 1-3 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan) under the provisions of the Budapest Treaty, and received an accession number of FERM BP-1539.

The DNA of the present invention is preferably ligated to a vector DNA autonomously replicable in a cell of Escherichia coli and/or coryneform bacteria to form a recombinant DNA. By introducing this recombinant DNA into an Escherichia coli cell, the subsequent procedure can be made easy. The vector autonomously replicable in Escherichia coli cells is preferably a plasmid vector autonomously replicable in the host cell, and examples thereof include pUC19, pUC18, pBR322, pHSG299, pHSG399, pHSG398, RSF1010 and so forth.

As the vector autonomously replicable in coryneform bacterium cells, there can be mentioned pAM330 (refer to Japanese Patent Laid-open (Kokai) No. 58-67699/1983), pHM1519 (refer to Japanese Patent Laid-open (Kokai) No. 58-77895/1983) and so forth. Moreover, if a DNA fragment having an ability to make a plasmid autonomously replicable in coryneform bacteria is taken out from these vectors and inserted into the aforementioned vectors for Escherichia coli, they can be used as a so-called shuttle vector autonomously replicable in both of Escherichia coli and coryneform bacteria. Examples of such a shuttle vector include those mentioned below. There are also indicated microorganisms which harbors each vector, and accession numbers thereof at the international depository are shown in the parentheses, respectively.

pAJ655 Escherichia coli AJ11882 (FERM BP-136)

Corynebacterium glutamicum SR8201(ATCC39135)

pAJ1844 Escherichia coli AJ11883(FERM BP-137)

Corynebacterium glutamicum SR8202(ATCC39136)

pAJ611 Escherichia coli AJ11884(FERM BP-138)

pAJ3148 Corynebacterium glutamicum SR8203(ATCC39137)

pAJ440 Bacillus subtilis AJ11901(FERM BP-140)

pHC4 Escherichia coli AJ12617(FERM BP-3532)

In order to prepare recombinant DNA by ligating the gene coding for GMP synthetase and a vector which can function in a cell of coryneform bacterium, the vector is digested by restriction enzyme(s) corresponding to the termini of the gene coding for GMP synthetase. Ligation is generally performed by using a ligase such as T4 DNA ligase.

To introduce the recombinant DNA prepared as described above to a coryneform bacterium, any known transformation methods can be employed. For instance, employable are a method of treating recipient cells with calcium chloride so as to increase-the permeability of DNA, which has been reported for Escherichia coli K-12 [see Mandel, M. and Higa, A., J. Mol. Biol., 53, 159 (1970)]; and a method of preparing competent cells from cells which are at the growth phase followed by introducing the DNA thereinto, which has been reported for Bacillus subtilis [see Duncan, C. H., Wilson, G. A. and Young, F. E., Gene, 1, 153 (1977)]. In addition to these, also employable is a method of making DNA-recipient cells into the protoplast or spheroplast which can easily take up recombinant DNAs followed by introducing the recombinant DNA into the cells, which is known to be applicable to Bacillus subtilis, actinomycetes and yeasts [see Chang, S. and Choen, S. N., Molec. Gen. Genet., 168, 111 (1979); Bibb, M. J., Ward, J. M. and Hopwood, O. A., Nature, 274, 398 (1978); Hinnen, A., Hicks, J. B. and Fink, G. R., Proc. Natl. Sci., USA, 75, 1929 (1978)]. The electric pulse method can be also applied (refer to Japanese Patent Publication Laid-Open No. 2-207791).

A microorganism that is transformed with the DNA of the present invention can be utilized for the production of GMP synthetase. Moreover, since a microorganism, for example Brevibacterium lactofermentum, transformed with the DNA of the present invention and has enhanced GMP synthetase activity is excellent in the ability to generate GMP from XMP, it can be used for the production of GMP by fermentation or enzymatic process utilizing bacterial cells.

According to the present invention, there is provided a GMP synthetase derived from Brevibacterium lactofermentum and a gene coding for it. The GMP synthetase can be used for the production of GMP. A transformant that harbors the gene can be used for the production of GMP synthetase or GMP.

BRIEF EXPLANATION OF THE DRAWING

FIG. 1 graphically shows thermostability of GMP synthetase of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, the present invention will be explained more specifically with reference to the following examples.

EXAMPLE 1

Isolation of GMP Synthetase Gene of Brevibacterium lactofermentum (guaA)

Genes corresponding to guaA were previously cloned from several kinds of organisms such as Escherichia coli, Bacillus subtilis, Corynebacterium ammonia genes, Borrelia burgdorferi and Dictyostelium discoideum. Based on alignment of GMP synthetases deduced from the nucleotide sequences of these genes, a plurality of regions conserved in the enzymes were discovered. Then, a part of the guaA gene of Brevibacterium lactofermentum was obtained by PCR on the basis of the amino acid sequences of these conserved regions.

The PCR primers were designed by selecting such a region that the number of corresponding codons should become as few as possible, and referring to occurring frequency of the codons in Brevibacterium lactofermentum. The sequences of produced primers are shown below. In the following sequences, Y represents mixture of T and C, R represents mixture of G and A, and W represents mixture of A and T.

(1) Primer 1

5′-WTCCCAWTCGATRGT-3′ (SEQ ID NO: 3)

(2) Primer 2

5′-CACCACAACGTYGGY-3′ (SEQ ID NO: 4)

(3) Primer 3

5′-RCCRACGTTGGGTG-3′ (SEQ ID NO: 5)

(4) Primer 4

5′-TGGATGTCYCACGGY-3′ (SEQ ID NO: 6)

(5) Primer 5

5′-TGGATGAGCCACGGY-3′ (SEQ ID NO: 7)

PCR was performed by using the aforementioned primers and chromosomal DNA of the Brevibacterium lactofermentum ATCC13869 strain as a template. Reaction conditions are shown in Table 1.

TABLE 1 PCR reaction condition Reaction Primer Reaction condition Cycle number 1 1, 2 94° C. for 30 seconds, 30 45° C. for 30 seconds, 72° C. for 2 minutes 2 1, 2 94° C. for 30 seconds, 40 45° C. for 30 seconds, 72° C. for 2 minutes 3 4, 5, 1 94° C. for 30 seconds, 40 45° C. for 30 seconds, 72° C. for 2 minutes 4 4, 5, 3 94° C. for 30 seconds, 40 45° C. for 30 seconds, 72° C. for 2 minutes

As a result of the aforementioned PCR, no reaction product with the desired size was obtained in Reaction 1. In Reactions 2, 3, and 4, reaction products having sizes of about 0.5 kbp, about 1.2 kbp and about 0.7 kbp, respectively, were obtained. However, production of a plurality of reaction products with sizes other than the target sizes was observed in each of Reactions 2, 3 and 4. Therefore, each reaction product was separated by agarose gel electrophoresis, and only the reaction product with the target size were recovered.

Each of the recovered reaction products was ligated to TA cloning vector (Invitrogen). By using the obtained recombinant plasmid as a template, the nucleotide sequence of each PCR product was determined. In this experiment, the PCR products of about 0.5 kbp and about 1.2 kbp among the aforementioned PCR products were used as templates for the nucleotide sequence determination. The nucleotide sequence was determined by using Big Dye Terminator Cycle Sequencing Kit (Perkin Elmer) and Genetic Analyzer 310 (Perkin Elmer).

As a result, it was found that the fragment of about 1.2 kbp overlapped the fragment of about 0.5 kbp, and the amino acid sequence deduced from the nucleotide sequence of the obtained region showed high homology to the amino acid sequences of known GMP synthetases derived from other organisms. Therefore, it was determined that the PCR products obtained above were highly possibly parts of the target gene.

Therefore, it was then attempted to obtain upstream and downstream regions of the obtained region. They were obtained by the cassette-ligation mediated PCR (Molecular and Cellular Probes, 6, 467-475). The actual operation was performed by using a TaKaRa LA PCR in vitro Cloning Kit (Takara Shuzo) according to the instruction attached to the kit.

The PCR primers used for obtaining the upstream region, which were specific for the known region, were:

5′-TGCTCTAGACCTGCGATCTCAGTGAGGAAG-3′ (SEQ ID NO: 8) for the first reaction, and

5′-CAGGGTGGTACTGCACGCCAGCCATTTTGC-3′ (SEQ ID NO: 9) for the second reaction.

The PCR primers used for obtaining the downstream region, which were specific for the known region, were:

5′-CTCTGTTGGAGTCCAAGGTGACGGCCGCAG-3′ (SEQ ID NO: 10) for the first reaction, and

5′-GTATCTTCCGAAGACGCAATGACCGCCGAC-3′ (SEQ ID NO: 11) for the second reaction.

The cassettes used were those for EcoRI, HindIII, PstI, SalI and XbaI. Each cassette was ligated to chromosomal DNA of the Brevibacterium lactofermentum ATCC13869 strain that was digested with a restriction enzyme corresponding to each of those cassettes, and PCR was performed by using aforementioned primers and cassette primers attached to the aforementioned kit. As a result, when cassettes for EcoRI, HindIII, PstI, and SalI were used in the reactions aiming at obtaining upstream regions, reaction products of about 1.5 kbp, about 0.5 kbp, about 1.5 kbp and about 1.0 kbp, respectively, were obtained. When nucleotide sequences of these products were determined, it was found that all of the products contained the same sequence.

Further, when cassettes for EcoRI, HindIII and XbaI were used in the reactions aiming at obtaining downstream regions, reaction products of about 1.2 kbp, about 0.5 kbp and about 1.2 kbp, respectively, were obtained. When nucleotide sequences of these products were determined, it was found that all of the products contained the same sequence.

The sequences obtained as described above were ligated taking into account the overlap regions to obtain a sequence which consisted of 3390 bases containing a region which could code for a protein consisting of 523 amino acid residues. This protein consisting of the 523 amino acid residues showed high homology to the amino acid sequences of known GMP synthetases derived from other organisms over the full length. Therefore, it was considered that the target guaA gene could be obtained. The homology between the thus obatined guaA gene and E. coil guaA determined by Lipman-Pearson method (Science, Vol.227, 1435-1441 (1985) is 55.7% in the nucleotide sequence level.

EXAMPLE 2

Expression of Brevibacterium lactofermentum guaA in Escherichia coli

In order to confirm that the gene obtained in Example 1 was the target guaA gene, that gene was introduced into Escherichia coli, and expressed. From the transformant, a cell-free extract was prepared, and its GMP synthetase activity was confirmed. The expression of the guaA gene in Escherichia coli was performed as follows.

PCR primers each added with the SD (Shine-Dalgarno) sequence and a restriction enzyme recognition site were designed based on the sequence obtained in Example 1. By using these primers and chromosomal DNA of Brevibacterium lactofermentum ATCC13869 as a template, PCR was performed. The sequences of the primers used above are shown below.

5′-CTCGTCGACAAGGAAAAAGACGTATGAGCCTTCAGACAAATCATCGCCC-3′ (SEQ ID NO: 12)

5′-CTCGCATGCTTAATCCCATTCGATGGTTCCTGGTGGCTTGGAGGTTACGTCC-3′ (SEQ ID NO: 13)

The obtained PCR product was digested with restriction enzymes that could digest the restriction sites added to the primers, and ligated to a vector, pUC18 (Takara Shuzo), digested with the same restriction enzymes. In this case, the target gene was ligated in the forward direction as to the direction of transcription by lac promoter present in the vector. Escherichia coli JM109 was transformed with the plasmid produced as described above.

The obtained transformant was cultured overnight in LB medium containing 50 μg/ml of ampicillin and 1 mM IPTG with shaking, then collected by centrifugation, and washed with Buffer A (20 mM potassium phosphate buffer (pH 7.5), 1 mM dithiothreitol (DTT)). The washed cells were suspended in the same buffer, and disrupted by sonication. After the sonication, cells not disrupted and other substances were removed by centrifugation to obtain a cell-free extract.

Measurement of GMP synthetase activity of the cell-free extract was performed in Reaction mixture A having the following composition: 100 MM Tris-HCl, pH 8.3, 1 mM DTT, 25 mM XMP, 25 mM ATP, 50 mM MgCl₂ and 50 mM L-glutamine. The reaction was allowed at 30° C. for 10 minutes, and then stopped by addition of 50-fold volume of 100 mM EDTA. Analysis and quantification of the reaction product were performed by HPLC. Analysis condition was as follows.

Column: Asahipak GS-220 (diameter: 7.6 mm, 50 cm)

Eluate: 0.2 M NaH₂PO₄ (pH 3.98)

Temperature: 50° C.

Flow rate: 1.5 ml/minute

Detection: Uv absorption (254 nm)

The quantification of proteins was performed by using Protein Assay Kit (Bio-Rad Laboratories). When the GMP synthetase activity of the prepared cell-free extract was measured with these conditions, conversion of XMP into GMP was observed with a cell-free extract prepared from the strain which was introduced with the obtained gene. Thus, the target activity was confirmed.

EXAMPLE 3

Characterization of Brevibacterium lactofermentum guaA Gene Product

Production of GMP from XMP was also observed in a reaction utilizing, as a GMP synthetase source, a cell-free extract prepared from Escherichia coli JM109 in which the guaA gene described in Example 2 was expressed, and utilizing (NH₄)₂SO₄ instead of L-glutamine so that ammonia should be the amino group donor. Then, Km values of the enzyme were determined for the amino group donors, L-glutamine and ammonia. As a result, Km values for L-glutamine and ammonia were 9.6 mM and 8.2 mM, respectively. That is, substantially the same values were obtained for the both substrates.

The ammonia concentration was calculated in accordance with the equation of Henderson-Hasselbach using pKa of ammonia, 9.3, and pH of reaction mixture, 8.0. When pH characteristics of the enzyme was determined, the maximum activity was observed around pH 6.5 with L-glutamine as the amino group donor, and around pH 8.0-9.0 with ammonia as the amino group donor, which was supplied by a constant amount of (NH₄)₂SO₄.

When the thermostability of the enzyme was examined, the result shown in FIG. 1 was obtained. The thermostability was determined by maintaining a cell-free extract at each temperature shown in FIG. 1 for 15 minutes, then measuring residual activity at 30° C., and calculating a relative activity to the activity obtained by using a cell-free extract maintained at 4° C. As shown in FIG. 1, the enzyme was stable at least up to 23° C.

                   #             SEQUENCE LISTING <160> NUMBER OF SEQ ID NOS:   13 <210> SEQ ID NO 1 <211> LENGTH: 3390 <212> TYPE: DNA <213> ORGANISM: Brevibacterium lactofermentum (Corneybac #terium       glutamicum) <220> FEATURE: <221> NAME/KEY: CDS <222> LOCATION: (887)..(2455) <400> SEQUENCE: 1 gaattccacc gcctgggaac gattacagca gtggcggaat ctatgaacta ca #gtcgttct     60 gcgatctccc aacaaatggc gctgctggaa aaagaaattg gtgtgaaact ct #ttgaaaaa    120 agcggccgaa acctctactt cacagaacaa ggcgaagtgt tggcctcaga aa #cacatgcg    180 atcatggcag cagtcgatca cgcccgcgca gccgtcctag attcgatgtc tg #aagtatcc    240 ggaacgctga aagtcacctc cttccaatcc ctgctgttca cccttgcccc ga #aagccatc    300 gcgcgcctga ccgagaaata cccacacctg caagtagaaa tctcccaact ag #aagtcacc    360 gcagcgctcg aagaactccg cgcccgccgc gtcgacgtcg cactcggtga gg #aatacccc    420 gtggaagttc ccctcgttga tgccagcatt caccgcgaag tcctcttcga ag #accccatg    480 ctgctggtca ccccagaaag cggtccatac tccggcctca ccctgccaga ac #tccgcgac    540 atccccatcg ccatcgaccc gcccgacctc cccgcaggcg aatgggtcca ta #ggctctgc    600 cggcgcgccg ggtttgagcc ccgcgtgacc tttgaaacca gcgatcccat gc #tccaggca    660 cacctcgtgc gcagcggttt ggccgtgaca ttttccccca cactgctcac cc #cgatgctg    720 gaaggcgtgc acatccagcc gctgcccggc aaccccacgc gcacgctcta ca #ccgcggtc    780 agggaagggc gccagaggca tccagccatt aaagcttttc gacgaaccct cc #gcccatgt    840 ggccaaagaa tcttatttgg aggctcgtct agtagagtga gttctt gtg  #agc ctt       895                    #                   #               Val Ser  #Leu                    #                   #               1 cag aca aat cat cgc cca gta ctc gtc gtt ga #c ttc ggc gca cag tac      943 Gln Thr Asn His Arg Pro Val Leu Val Val As #p Phe Gly Ala Gln Tyr     5               #     10              #     15 gcg cag ctg atc gca cgt cgt gtg cgt gag gc #c ggc atc tac tcc gaa      991 Ala Gln Leu Ile Ala Arg Arg Val Arg Glu Al #a Gly Ile Tyr Ser Glu 20                   #25                   #30                   #35 gtc atc ccg cac acc gcc acc gca gac gat gt #g cgc gct aaa aat gca     1039 Val Ile Pro His Thr Ala Thr Ala Asp Asp Va #l Arg Ala Lys Asn Ala                 40   #                45   #                50 gca gcc ctc gtc ctt tcc ggt ggt cca tcc tc #c gtg tat gcc gag gga     1087 Ala Ala Leu Val Leu Ser Gly Gly Pro Ser Se #r Val Tyr Ala Glu Gly             55       #            60       #            65 gca cca tcc ctt gac gct gag atc cta gat ct #c gga ttg cca gta ttt     1135 Ala Pro Ser Leu Asp Ala Glu Ile Leu Asp Le #u Gly Leu Pro Val Phe         70           #        75           #        80 ggc att tgc tac ggc ttc caa gcc atg acc ca #c gcg ctt ggt ggc acc     1183 Gly Ile Cys Tyr Gly Phe Gln Ala Met Thr Hi #s Ala Leu Gly Gly Thr     85               #    90               #    95 gtt gcc aac acc ggt aag cgc gaa tac gga cg #c acc gac atc aac gtt     1231 Val Ala Asn Thr Gly Lys Arg Glu Tyr Gly Ar #g Thr Asp Ile Asn Val 100                 1 #05                 1 #10                 1 #15 gcc ggt ggc gtc ctc cac gaa ggc ctc gag gc #c tgc cac aag gtg tgg     1279 Ala Gly Gly Val Leu His Glu Gly Leu Glu Al #a Cys His Lys Val Trp                 120   #               125   #               130 atg agc cac ggc gac gcc gtc tct gaa gcc cc #a gaa ggt ttc gta gtc     1327 Met Ser His Gly Asp Ala Val Ser Glu Ala Pr #o Glu Gly Phe Val Val             135       #           140       #           145 acc gct tcc tcc gaa ggt gcg cct gtc gca gc #t ttc gaa aac aag gaa     1375 Thr Ala Ser Ser Glu Gly Ala Pro Val Ala Al #a Phe Glu Asn Lys Glu         150           #       155           #       160 cgc aaa atg gct ggc gtg cag tac cac cct ga #g gtg ctg cac tca cca     1423 Arg Lys Met Ala Gly Val Gln Tyr His Pro Gl #u Val Leu His Ser Pro     165               #   170               #   175 cac ggc cag gca gtt ctg acc cgc ttc ctc ac #t gag atc gca ggt cta     1471 His Gly Gln Ala Val Leu Thr Arg Phe Leu Th #r Glu Ile Ala Gly Leu 180                 1 #85                 1 #90                 1 #95 gag cag aac tgg acc gca gca aac atc gct ga #a gaa ctc atc gaa aag     1519 Glu Gln Asn Trp Thr Ala Ala Asn Ile Ala Gl #u Glu Leu Ile Glu Lys                 200   #               205   #               210 gtc cgc gag cag atc ggc gaa gat ggc cgc gc #t att tgt ggc cta tcc     1567 Val Arg Glu Gln Ile Gly Glu Asp Gly Arg Al #a Ile Cys Gly Leu Ser             215       #           220       #           225 ggt ggt gtg gac tcc gct gtt gcc ggt gct tt #g gtg cag cgt gca att     1615 Gly Gly Val Asp Ser Ala Val Ala Gly Ala Le #u Val Gln Arg Ala Ile         230           #       235           #       240 ggt gac cgt ttg acc tgt gtc ttt gtt gac ca #c ggt ctg ctg cgt gcc     1663 Gly Asp Arg Leu Thr Cys Val Phe Val Asp Hi #s Gly Leu Leu Arg Ala     245               #   250               #   255 ggt gag cgc gag cag gtg gaa aaa gac ttc gt #c gca gca acc ggc gcc     1711 Gly Glu Arg Glu Gln Val Glu Lys Asp Phe Va #l Ala Ala Thr Gly Ala 260                 2 #65                 2 #70                 2 #75 aag ctg gtt acc gtt gat gag cgt caa gca tt #c ctg tcc aag ctg gcc     1759 Lys Leu Val Thr Val Asp Glu Arg Gln Ala Ph #e Leu Ser Lys Leu Ala                 280   #               285   #               290 gga gtt acc gaa cca gaa gca aag cgc aag gc #t atc ggc gct gag ttc     1807 Gly Val Thr Glu Pro Glu Ala Lys Arg Lys Al #a Ile Gly Ala Glu Phe             295       #           300       #           305 atc cgc tcc ttc gag cgc gca gtt gcc ggt gt #g ctg gaa gat gca cca     1855 Ile Arg Ser Phe Glu Arg Ala Val Ala Gly Va #l Leu Glu Asp Ala Pro         310           #       315           #       320 gaa ggt tcc acc gtg gac ttc cta gtt cag gg #c acc ctg tac cca gac     1903 Glu Gly Ser Thr Val Asp Phe Leu Val Gln Gl #y Thr Leu Tyr Pro Asp     325               #   330               #   335 gtc gtg gaa tcc ggt ggt gga tct ggt acc gc #a aac atc aag agc cac     1951 Val Val Glu Ser Gly Gly Gly Ser Gly Thr Al #a Asn Ile Lys Ser His 340                 3 #45                 3 #50                 3 #55 tac aac gtc ggt gga ctg cca gac gat gtg ga #a ttc aag ctt gtt gag     1999 Tyr Asn Val Gly Gly Leu Pro Asp Asp Val Gl #u Phe Lys Leu Val Glu                 360   #               365   #               370 cca ctg cgt gac ctc ttc aaa gac gaa gtc cg #t gcc gtt ggc cgt gaa     2047 Pro Leu Arg Asp Leu Phe Lys Asp Glu Val Ar #g Ala Val Gly Arg Glu             375       #           380       #           385 ctt ggc ctg cct gag gaa atc gtt ggc cgc ca #g cca ttc cca gga cca     2095 Leu Gly Leu Pro Glu Glu Ile Val Gly Arg Gl #n Pro Phe Pro Gly Pro         390           #       395           #       400 gga ctt ggt atc cgc atc atc ggt gaa gtc ac #c gaa gag cgc ctg gaa     2143 Gly Leu Gly Ile Arg Ile Ile Gly Glu Val Th #r Glu Glu Arg Leu Glu     405               #   410               #   415 acc ctc cgc cac gct gac ctg atc gcc cgc ac #c gag ctc acc gaa gcc     2191 Thr Leu Arg His Ala Asp Leu Ile Ala Arg Th #r Glu Leu Thr Glu Ala 420                 4 #25                 4 #30                 4 #35 gga ctc gac ggc gtg atc tgg cag tgc cca gt #c gtc ctc ttg gca gat     2239 Gly Leu Asp Gly Val Ile Trp Gln Cys Pro Va #l Val Leu Leu Ala Asp                 440   #               445   #               450 gtc cgc tct gtt gga gtc caa ggt gac ggc cg #c acc tac gga cac cca     2287 Val Arg Ser Val Gly Val Gln Gly Asp Gly Ar #g Thr Tyr Gly His Pro             455       #           460       #           465 atc gtg ctg cgc cca gta tct tcc gaa gac gc #a atg acc gcc gac tgg     2335 Ile Val Leu Arg Pro Val Ser Ser Glu Asp Al #a Met Thr Ala Asp Trp         470           #       475           #       480 acc cgc ttg cca tac gaa gtc ctg gag aag at #c tcc acc cgc atc acc     2383 Thr Arg Leu Pro Tyr Glu Val Leu Glu Lys Il #e Ser Thr Arg Ile Thr     485               #   490               #   495 aac gaa gtt cca gac gta aac cgc gtg gtt tt #g gac gta acc tcc aag     2431 Asn Glu Val Pro Asp Val Asn Arg Val Val Le #u Asp Val Thr Ser Lys 500                 5 #05                 5 #10                 5 #15 cca cca gga acc atc gaa tgg gag taggccttaa at #gagccttc gttaagcggc    2485 Pro Pro Gly Thr Ile Glu Trp Glu                 520 aatcacctta tcggtgattg ccgctttccc atttctccgg gttttctgga ac #tttttggg   2545 cgtatgctgg gaatgatctt attattttga tttcagaaag caggagagac ca #gatgagcg   2605 aaatccttga aacctactgg gcaccccact tcggaaacac cgatgaagcc gc #agcactcg   2665 tttcatactt ggcacaagct tccggtgatc ctattgaggt tcacaccctg tt #cggggatt   2725 taggtttaga cggactctct ggaaactaca ccgacactga gatcgacggc ta #cggcgacg   2785 cattcctgct ggttgcagca ctagcagtgt tgatggctga aaacaaagca tc #cggcggcg   2845 tgaatctggg tgaagttggg ggagctgata aatcgatccg gctgcatgtt ga #atccaagg   2905 aaaacaccca gatcaacacc gcattgaagt actttgcgct ttccccagaa ga #ccacgcag   2965 cggcagatcg cttcgatgag gatgacctgt ctgagcttgc caacttgagt ga #agagctgc   3025 gcggacagct ggactaattg ctgcccgttt aaggagtccg attcttcaga tg #agtagatg   3085 cctccaagtg aggctgggag gctcttagaa tcgattctga gagggcactt tt #tattggcc   3145 ttggggtgga atctgcaacg gaccaaacca cactgcccac ggatcctaaa aa #ggggatcc   3205 gtgggcagtc tggtttggtt attcgacctt caaaccggtc acacatgccc ac #gaacccca   3265 ataatcggat tcgtgggcac tctggtttgg ttaccaggat gggttagtca tt #ctgatcag   3325 cgaattccac gttcacatcg ccaattccag agttcacaac cagattcagc at #tggacctt   3385 ctaga                  #                   #                   #          3390 <210> SEQ ID NO 2 <211> LENGTH: 523 <212> TYPE: PRT <213> ORGANISM: Brevibacterium lactofermentum (Corneybac #terium       glutamicum) <400> SEQUENCE: 2 Val Ser Leu Gln Thr Asn His Arg Pro Val Le #u Val Val Asp Phe Gly 1               5    #                10   #                15 Ala Gln Tyr Ala Gln Leu Ile Ala Arg Arg Va #l Arg Glu Ala Gly Ile             20       #            25       #            30 Tyr Ser Glu Val Ile Pro His Thr Ala Thr Al #a Asp Asp Val Arg Ala         35           #        40           #        45 Lys Asn Ala Ala Ala Leu Val Leu Ser Gly Gl #y Pro Ser Ser Val Tyr     50               #    55               #    60 Ala Glu Gly Ala Pro Ser Leu Asp Ala Glu Il #e Leu Asp Leu Gly Leu 65                   #70                   #75                   #80 Pro Val Phe Gly Ile Cys Tyr Gly Phe Gln Al #a Met Thr His Ala Leu                 85   #                90   #                95 Gly Gly Thr Val Ala Asn Thr Gly Lys Arg Gl #u Tyr Gly Arg Thr Asp             100       #           105       #           110 Ile Asn Val Ala Gly Gly Val Leu His Glu Gl #y Leu Glu Ala Cys His         115           #       120           #       125 Lys Val Trp Met Ser His Gly Asp Ala Val Se #r Glu Ala Pro Glu Gly     130               #   135               #   140 Phe Val Val Thr Ala Ser Ser Glu Gly Ala Pr #o Val Ala Ala Phe Glu 145                 1 #50                 1 #55                 1 #60 Asn Lys Glu Arg Lys Met Ala Gly Val Gln Ty #r His Pro Glu Val Leu                 165   #               170   #               175 His Ser Pro His Gly Gln Ala Val Leu Thr Ar #g Phe Leu Thr Glu Ile             180       #           185       #           190 Ala Gly Leu Glu Gln Asn Trp Thr Ala Ala As #n Ile Ala Glu Glu Leu         195           #       200           #       205 Ile Glu Lys Val Arg Glu Gln Ile Gly Glu As #p Gly Arg Ala Ile Cys     210               #   215               #   220 Gly Leu Ser Gly Gly Val Asp Ser Ala Val Al #a Gly Ala Leu Val Gln 225                 2 #30                 2 #35                 2 #40 Arg Ala Ile Gly Asp Arg Leu Thr Cys Val Ph #e Val Asp His Gly Leu                 245   #               250   #               255 Leu Arg Ala Gly Glu Arg Glu Gln Val Glu Ly #s Asp Phe Val Ala Ala             260       #           265       #           270 Thr Gly Ala Lys Leu Val Thr Val Asp Glu Ar #g Gln Ala Phe Leu Ser         275           #       280           #       285 Lys Leu Ala Gly Val Thr Glu Pro Glu Ala Ly #s Arg Lys Ala Ile Gly     290               #   295               #   300 Ala Glu Phe Ile Arg Ser Phe Glu Arg Ala Va #l Ala Gly Val Leu Glu 305                 3 #10                 3 #15                 3 #20 Asp Ala Pro Glu Gly Ser Thr Val Asp Phe Le #u Val Gln Gly Thr Leu                 325   #               330   #               335 Tyr Pro Asp Val Val Glu Ser Gly Gly Gly Se #r Gly Thr Ala Asn Ile             340       #           345       #           350 Lys Ser His Tyr Asn Val Gly Gly Leu Pro As #p Asp Val Glu Phe Lys         355           #       360           #       365 Leu Val Glu Pro Leu Arg Asp Leu Phe Lys As #p Glu Val Arg Ala Val     370               #   375               #   380 Gly Arg Glu Leu Gly Leu Pro Glu Glu Ile Va #l Gly Arg Gln Pro Phe 385                 3 #90                 3 #95                 4 #00 Pro Gly Pro Gly Leu Gly Ile Arg Ile Ile Gl #y Glu Val Thr Glu Glu                 405   #               410   #               415 Arg Leu Glu Thr Leu Arg His Ala Asp Leu Il #e Ala Arg Thr Glu Leu             420       #           425       #           430 Thr Glu Ala Gly Leu Asp Gly Val Ile Trp Gl #n Cys Pro Val Val Leu         435           #       440           #       445 Leu Ala Asp Val Arg Ser Val Gly Val Gln Gl #y Asp Gly Arg Thr Tyr     450               #   455               #   460 Gly His Pro Ile Val Leu Arg Pro Val Ser Se #r Glu Asp Ala Met Thr 465                 4 #70                 4 #75                 4 #80 Ala Asp Trp Thr Arg Leu Pro Tyr Glu Val Le #u Glu Lys Ile Ser Thr                 485   #               490   #               495 Arg Ile Thr Asn Glu Val Pro Asp Val Asn Ar #g Val Val Leu Asp Val             500       #           505       #           510 Thr Ser Lys Pro Pro Gly Thr Ile Glu Trp Gl #u         515           #       520 <210> SEQ ID NO 3 <211> LENGTH: 15 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: (1)..() <223> OTHER INFORMATION: w=a or t <221> NAME/KEY: misc_feature <222> LOCATION: (13)..() <223> OTHER INFORMATION: r=g or a <221> NAME/KEY: misc_feature <222> LOCATION: (7)..() <223> OTHER INFORMATION: w=a or t <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 3 wtcccawtcg atrgt               #                   #                   #    15 <210> SEQ ID NO 4 <211> LENGTH: 15 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: (12)..() <223> OTHER INFORMATION: y=t or c <221> NAME/KEY: misc_feature <222> LOCATION: (15)..() <223> OTHER INFORMATION: y=t or c <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 4 caccacaacg tyggy               #                   #                   #    15 <210> SEQ ID NO 5 <211> LENGTH: 14 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: (1)..() <223> OTHER INFORMATION: r=g or a <221> NAME/KEY: misc_feature <222> LOCATION: (4)..() <223> OTHER INFORMATION: r=g or a <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 5 rccracgttg ggtg               #                   #                   #     14 <210> SEQ ID NO 6 <211> LENGTH: 15 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: (9)..() <223> OTHER INFORMATION: y=t or c <221> NAME/KEY: misc_feature <222> LOCATION: (15)..() <223> OTHER INFORMATION: y=t or c <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 6 tggatgtcyc acggy               #                   #                   #    15 <210> SEQ ID NO 7 <211> LENGTH: 16 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: (16)..() <223> OTHER INFORMATION: y=t or c <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 7 ttggatgagc cacggy              #                   #                   #    16 <210> SEQ ID NO 8 <211> LENGTH: 30 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 8 tgctctagac ctgcgatctc agtgaggaag          #                   #           30 <210> SEQ ID NO 9 <211> LENGTH: 30 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 9 cagggtggta ctgcacgcca gccattttgc          #                   #           30 <210> SEQ ID NO 10 <211> LENGTH: 30 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 10 ctctgttgga gtccaaggtg acggccgcag          #                   #           30 <210> SEQ ID NO 11 <211> LENGTH: 30 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 11 gtatcttccg aagacgcaat gaccgccgac          #                   #           30 <210> SEQ ID NO 12 <211> LENGTH: 49 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 12 ctcgtcgaca aggaaaaaga cgtatgagcc ttcagacaaa tcatcgccc   #               49 <210> SEQ ID NO 13 <211> LENGTH: 52 <212> TYPE: DNA <213> ORGANISM: Artificial/Unknown <220> FEATURE: <221> NAME/KEY: misc_feature <222> LOCATION: ()..() <223> OTHER INFORMATION: synthetic DNA <400> SEQUENCE: 13 ctcgcatgct taatcccatt cgatggttcc tggtggcttg gaggttacgt cc #             52 

What is claimed is:
 1. An isolated DNA which codes for a protein defined as follows: (A) a protein which has the amino acid sequence of SEQ ID NO: 2, or (B) a protein which has 90% homology to the amino acid sequence of SEQ ID NO: 2 and has GMP synthetase activity.
 2. The isolated DNA according to claim 1, which is a DNA defined as follows: (A) a DNA which has the nucleotide sequence comprising at least the nucleotide sequence of the nucleotide numbers 887 to 2455 in SEQ ID NO: 1; or (B) a DNA which is hybridizable with a nucleotide sequence comprising at least the nucleotide sequence of the nucleotide numbers 887 to 2455 in SEQ ID NO: 1 under a stringent conditions, and codes for a protein having GMP synthetase activity wherein said stringent conditions comprise washing in 1×SSC, and 0.1% SDS at 60° C.
 3. A transformant which is introduced with the DNA according to claim 1 in a form that allows expression of a protein encoded by the DNA.
 4. A transformant which is introduced with the DNA according to claim 2 in a form that allows expression of a protein encoded by the DNA. 